Keeping data all-optical would significantly speed up transmission of large amounts of data, such as detailed medical images, telepresence applications, high-speed image recognition, and high-definition video.

Engineers have built devices that can switch optical signals by manipulating mirrors or bubbles to redirect the light beams. The Georgia Tech team, in contrast, designed molecules that could theoretically switch optical signals in just a few femtoseconds, versus the microseconds needed by systems that use physical mechanisms to redirect the light.

The team started its design process by looking at a class of organic molecules called polymethine dyes. These brightly colored molecules have unusual properties that allow researchers to change the refractive index of the material by shining a light on it--and hence shift the phase of any light waves traveling through it. This gives them a way to control the modulation of light using only optical systems--no electricity needed.

Researchers had looked into using organic molecules for optical switching about 15 or 20 years ago because of their very fast response to electric and optical fields, says Larry Dalton, a chemist and electrical engineer who develops optical materials at the University of Washington. In fact, the intrinsic response time of organic molecules is between 10 and 100 terahertz, meaning that if the right material is found, data might be processed at those astonishing speed. However, no one was able to create organic materials that could shift the phase far enough without absorbing too much of the light wavelengths used in telecommunications systems. The dye created by the Georgia Tech team "is the first that allows you to change the index of refraction without light being lost," Dalton says. "You have the potential to move forward with practical applications now"--including improved methods of optically encoding data and all-optical computing, as well as ultrafast optical switching.

So far, the researchers have only measured the molecule's optical properties in a liquid solution. "The hard work comes now in taking these molecules and putting them into a material and making the switch," Marder says. The Georgia Tech chemists are already working on that task. While the dye itself is "not the easiest thing to make" and the material will ultimately be expensive, Marder says, any device will probably use only very small quantities.